Mechanistic insights into the degradation of poly (3-hydroxybutyrate) and its copolymers by Nocardiopsis dassonvillei NCIM 5124.

BACKGROUND: Poly (3-hydroxybutyrate) - PHB, a biodegradable polymer produced by numerous bacteria is a promising alternative to petrochemical plastics. A variety of microorganisms including Nocardiopsis dassonvillei NCIM 5124 can degrade PHB and its copolymers. Understanding the molecular mechanism involved in PHB degradation is essential for improving its biotechnological applications and optimizing bioplastic recycling. METHODS: The ability of N. dassonvillei NCIM 5124 to degrade PHB and its copolymers was demonstrated. To understand the underlying mechanistic aspects, reference-based transcriptome analysis, validation via quantitative polymerase chain reaction (qPCR), and in silico structural modeling were used. Comparisons were made between PHB, poly (3-hydroxybutyrate- co-3-hydroxyvalerate) - PHBV, or poly (3-hydroxybutyrate-co-3-hydroxyvalerate-co-3- hydroxyhexanoate) - PHBVH-grown cells while considering glucose-grown cells as reference samples. RESULTS: N. dassonvillei NCIM 5124 degraded PHB with the breakdown product being 3-hydroxybutyrate (3HB). Transcriptomic analysis revealed a significant upregulation of genes related to (i) signaling via the histidine kinase pathway, (ii) breakdown of PHB into monomeric 3-hydroxybutyrate - 3HB facilitated by PHB depolymerase and alpha/beta hydrolase (iii) transport of 3HB through the ATP-binding cassette (ABC) and major facilitator superfamily (MFS) proteins, (iv) further degradation of 3HB mediated by 3-hydroxybutyrate dehydrogenase, and (v) cell surface modification via the chaplin protein. The results were substantiated by qPCR analysis and structural modeling studies and a proposed mechanism by which the organism degrades PHB is suggested. CONCLUSIONS: The study provides insights into the probable mechanism by which N. dassonvillei NCIM 5124 degrades PHB and its copolymers. The tentatively identified signaling pathways, transport systems, and metabolic enzymes may serve as potential molecular targets for engineering microbial strains for sustainable bioplastic degradation and recycling.